PHYSICO-CHEMICAL PROPERTIES 63 



the acti\e principles. These observations could not be confirmed 

 in my laboratories. 



It may be concluded from the ^vork reviewed that the skin- 

 preparatory and reacting factors possess a considerable heat re- 

 sistance. The heat resistance may differ ^vith various microorgan- 

 isms and even strains of the same microorganism. It may also be 

 influenced by the mode of preparation of the material {i.e., 

 amount of autolysis, medium ingredients, etc.) . It is obvious 

 that the investigations just described have been undertaken in 

 order to determine ^vhetiier the active principles of the phenom- 

 enon are exo- or endotoxic in nature. The present generally ac- 

 cepted point of \'ie^v, to be discussed in more detail in Chapter x, 

 is, however, that the heat resistance of a bacterial toxic material 

 cannot be used as a clear-cut criterion for this differentiation even 

 among classical exotoxins. 



My present contention is that the active principles of the 

 phenomenon are secreted by the bacterial cell during the phases 

 of active growth and that remnants of these principles may be 

 also obtained through cell disintegration. The observations re- 

 corded here and subsequently in this chapter point to the possi- 

 bility that the ability of a bacterial cell to give off the active 

 principles depends on certain inherent characteristics differing in 

 various microorganisms and their strains. It may be plausible to 

 assimie that the active principles deri\ed from the bacterial cell 

 through its disintegration may prove to be more heat stabile be- 

 cause of some protective effect of the cell elements. 



THE EFFECT OF DIFFERENT HYDROGEN ION CONCENTRATIONS UPON 

 ACTIVE PRINCIPLES 



In my studies on the effect of acids and alkali upon the skin- 

 preparatory factors of B. typhosus, tryptic digest broth culture 

 filtrates were adjusted under sterile precautions to pH 9.0, 8.6, 

 7.6, 7.0, 6.6, 5.4 and 4.0. The final dilution of the filtrates of 

 various pH was 1:2. The filtrates of pH 9.0 and 4.0 were used on 

 the day of adjustment; those of pH 8.6, 7.6, 7.0, 6.6 and 5.4 were 

 injected t^venty-four hours after the adjustments. Before use, given 

 ainounts of filtrates of various pH were heated for one hour at 

 60° c. in the Arnold sterilizer and in the autoclave at 15 lbs. pres- 

 sure. Heated and non-heated filtrates of each pH ^vere tested for 

 skin-preparatory potency. The non-adjusted unheated filtrate was 



